docs: add example how to restore a raw device
docs: add example how to restore a raw device

also: do not use /dev/sda in case someone stupidly tries out the examples.
/dev/sdx should be safe for people who do not understand what they do.

edgimar/borg,RonnyPfannschmidt/borg,raxenak/borg,raxenak/borg,mhubig/borg,RonnyPfannschmidt/borg,RonnyPfannschmidt/borg,edgimar/borg,mhubig/borg,edgewood/borg,RonnyPfannschmidt/borg,edgewood/borg,edgimar/borg,RonnyPfannschmidt/borg,raxenak/borg,edgewood/borg,edgewood/borg,edgimar/borg,raxenak/borg,mhubig/borg